The inosinate synthesis is complex, beginning with a 5-phosphoribosyl-1-pyrophosphate (PRPP). In the first step, an amino group given by glutamine is attached at carbon 1 of PRPP. The resulting molecule is 5-phosphoribosylamine, which is highly unstable, with a half-life of 30 seconds at physiologic pH. 5-Phosphoribosylamine gains an amino acid (glycine), becoming glycinamide ribonucleotide (GAR). Then, N10-formyltetrahydrofolate (Tetrahydrofolate) transfers a formyl group to glycinamide ribonucleotide to form formyl glycinamide ribonucleotide (FGAR).

This figure shows the pathway described: IMP synthesis.

Using an ATP molecule, glutamine donates an ammonia[dubious– discuss] molecule which is added to the compound forming formylglycinamidine ribonucleotide. Another ATP molecule causes an intermolecular reaction that produces an imidazole ring (5-aminoimidazole ribonucleotide).

The next step of the pathway is adding bicarbonate to make carboxyaminoimidazole ribonucleotide by using ATP (it only happens in fungi and bacteria; high eukaryotes simply add CO2 to form the ribonucleotide). Then, the imidazole’s carboxylate group phosphatises and adds aspartate.

As we have just seen, a six-step process links glycine, formate, bicarbonate, glutamine, and aspartate to lead to an intermediate that contains almost all the required atoms to synthesize a purine ring. This intermediate removes fumarate, and a second formyl group from THF is added. The compound gets cycled and forms inosinate[dubious– discuss] after a sort of intermolecular reactions. Inosinate is the first intermediate in this synthesis pathway to have a whole purine ring.

Enzymes taking part in IMP synthesis constitute a multienzyme complex in the cell. Evidences demonstrate that there are multifunctional enzymes, and some of them catalyze non-sequential steps in the pathway.

Within a few steps inosinate becomes AMP or GMP. Both compounds are RNAnucleotides. AMP differs from inosinate by the replacement of IMP's carbon-6 carbonyl with an amino group. The interconversion of AMP and IMP occurs as part of the purine nucleotide cycle.[2] GMP is formed by the inosinate oxidation to xanthylate (XMP), and afterwards adds an amino group on carbon 2. Hydrogen acceptor on inosinate oxidation is NAD+. Finally, carbon 2 gains the amino group by spending an ATP molecule (which becomes AMP+2Pi). While AMP synthesis requires GTP, GMP synthesis uses ATP. That difference offers an important regulation possibility.

Glutamine-PRPP-amidotransferase

Inosinate takes part in the regulation of purine nucleotides biosynthesis[edit]

Inosinate and many other molecules inhibit the synthesis of 5-phosphorybosilamine from 5-phosphoribosyl-1-pyrophosphate (PRPP), disabling the enzyme that catalyzes the reaction: glutamine-5-phosphoribosyl-1-pyrophosphate-amidotransferase. In other words, when levels of inosinate are high, glutamine-5-phosphoribosyl-1-pyrophosphate-amidotransferase is inhibited, and, as a consequence, inosinate levels decrease. Also, as a result, adenylate and guanylate are not produced, which means that RNA synthesis cannot be completed because of the lack of these two important RNA nucleotides.